During the past few years there has been a substantial growth in the production of high strength paper and cloth products having a nonwoven, randomly oriented structure, bonded with a polymeric resin binder. Such products are finding wide use as high strength, high absorbency materials for disposable items such as consumer and industrial wipes/towels, diapers, surgical packs and gowns, industrial work clothing and feminine hygiene products. They are also used for durable products such as carpet and rug backings, apparel interlinings, automotive components and home furnishings, and for civil engineering materials such as road underlays. There are several ways to apply such a binder to these materials, including spraying, print binding and foam application. Further, depending on the end use, various ingredients such as catalysts, cross-linkers, surfactants, thickeners, dyes and flame retardant salts may also be incorporated into the binder system.
In the high speed, high volume manufacture of cellulosic products such as wet wipes, an important binder property is a fast cure rate, i.e., the finished product must reach substantially full tensile strength in a very short time after binder application, so that production rates are not unduly slowed down. In these products, such a property is usually obtained by using a binder which is either self cross-linkable or by incorporating an external cross-linker into the binder formulation. When this is done, the cross-linker apparently not only interacts with the binder monomers but with the hydroxyl groups on the cellulose fibers to quickly form very strong bonds.
At present, there are a number of available binder formulations which meet this requirement. However, these materials are typified by incorporating one or more constituents which, over some period of time, will emit levels of formaldehyde in an amount sufficient to cause skin and respiratory irritation in many people, particularly children. Most recently, several of the leading manufacturers of nonwoven cellulosic products have expressed a desire to replace such binders with products offering equivalent levels of performance in cellulose but without the emission of formaldehyde. Although a number of ostensibly zero formaldehyde or "0 CH.sub.2 O" cellulose binders have been proposed, they have either not been truly "0" in formaldehyde content or have not shown sufficiently fast cure rates to be acceptable in high volume production applications.